At present, the common method used for collecting the by-product gases is to seal-off all the oven openings except for the off-take pipe. The gases then must flow from the oven through the off-take pipe and thence to the collection main which discharges to a decanter tank in the by-product processing plant. During the charging operation, however, the charging ports on top of the oven must be uncovered to admit coal into the oven. As the coal drops into the oven, voluminous clouds of smoke escape from the charging ports to the atmosphere thereby causing a serious air pollution problem.
Various attempts have been made by coke oven operators to control smoke emissions during oven charging operations, one means being to impose a negative pressure on the oven by steam aspiration in the off-take pipe. When the steam pressure and steam flow through the aspiration nozzle are increased to produce a sufficient negative pressure in the oven as required to draw the smoke into the off-take pipe, however, several problems are encountered:
1. Greater quantities of particulate matter are also drawn into the off-take pipe thereby exceeding the allowable limits for quinolin insolubles in the by-products, PA1 2. Much of this particulate matter being large and dense as compared to the particles normally collected during the carbonization period, settle in the collecting main thus requiring more frequent cleaning or "spooning of the main", PA1 3. The increased smoke and gas flow through the off-take pipe results in higher operating temperatures in the off-take pipe causing the off-take piping, valves, and other component parts of the gas collection system to warp and bind, thereby resulting in numerous leaks and other maintenance problems.
Because of these problems, the steam pressure and flow through the aspiration nozzle must be greatly reduced or even not used at all during the oven charging operation thereby causing considerable quantities of smoke and gas to escape from the charging ports and thus, to contaminate the atmosphere.
Referring to the drawing of FIG. 1, the common means presently employed for collection of the off-gases from a by-product coke oven is through the vertical off-take pipe sections 1, 2, and 3 which convey the gases to a collection main. The vertical ascension sections 1 and 2 as well as the gooseneck section 3 are lined with firebrick 5 which provides thermal protection from the hot gases 6 being discharged from the oven 4. In addition, a heat shield 7 around the lower ascension pipe is commonly employed to protect workmen from radiated heat and to prevent accidental contact with the hot surface of the ascension pipe.
The operating phase performed in filling the coke oven with coal is commonly referred to as "charging the oven". An oven normally has three or four charging holes or ports located in the top of the oven which is the roof of the oven. A larry car having a like number of coal hoppers travels on rail across the top of the oven and is positioned above the oven to be charged so that the coal hoppers are aligned with the charging ports. Before the coal is dropped into the oven, a workman opens a steam valve which allows steam to flow through the aspirator nozzle 9. The high velocity of the steam flow 8 aspirates the hot gases from the ascension pipe thereby imposing a negative pressure on the oven. The hot gases rising in the ascension pipe are discharged into the collection main where the gases are cooled and the particulate matter settles to the bottom of the main.
The amount of particulates present in the gas as it is drawn from the oven, varies directly as the steam pressure and flow through the aspiration nozzle. If the amount of quinolin insolubles in the off-gases becomes excessive, the tar compound also present in the gas, become overly contaminated making them unacceptable for further processing. In addition, the larger particle sizes which are drawn from the oven with increased gas flow, settle to the bottom of the collection main and clog the main thereby requiring more frequent spooning of the main. In order that both conditions may be avoided, the steam pressure must accordingly be reduced to lower levels such that the steam aspiration becomes ineffective as an air pollution control means and hence most of the smoke and gas generated in the oven during charging, escape from the oven to the atmosphere through the oven charging ports.